German patent document DE 10 2004 044 145 B3 discusses a reflector module for a photometric gas sensor. The reflector module is configured as a cover for a bottom part on which an infrared radiation source and an infrared detector are mounted, a measuring gas being diffusible into the measuring volume covered by the reflector module. At least two reflective inner surfaces are formed on the reflector module in such a way that infrared radiation emitted by the infrared radiation source is deflectable along an absorption section onto the infrared detector. A concentration of the measuring gas is to be ascertainable with the aid of an analysis of the absorption of the infrared radiation along the absorption section.